1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head used in a thermally-assisted magnetic recording in which near-field light is applied to a magnetic recording medium to lower a coercivity thereof so as to record information, and a head gimbals assembly, a head arm assembly, and a magnetic disk unit which are provided with the thermally-assisted magnetic recording head.
2. Description of Related Art
A magnetic disk unit in the related art is used for writing and reading magnetic information (hereinafter, simply referred to as information). The magnetic disk unit is provided with, in the housing thereof, a magnetic disk in which information is stored, and a magnetic read write head which records information into the magnetic disk and reproduces information stored in the magnetic disk. The magnetic disk is supported by a rotary shaft of a spindle motor, which is fixed to the housing, and rotates around the rotary shaft. On the other hand, the magnetic read write head is formed on a side surface of a magnetic head slider provided on one end of a suspension, and the magnetic read write head includes a magnetic write element and a magnetic read element which have an air bearing surface (ABS) facing the magnetic disk. In particular, as the magnetic read element, a magneto-resistive (MR) element exhibiting magneto-resistive effect is generally used. The other end of the suspension is attached to an end of an arm which is rotatably supported by a fixed shaft installed upright in the housing.
When the magnetic disk unit is not operated, namely, when the magnetic disk does not rotate, the magnetic read write head is not located over the magnetic disk and is pulled off to the position away from the magnetic disk (unload state). When the magnetic disk unit is driven and the magnetic disk starts to rotate, the magnetic read write head is changed to a state where the magnetic read write head is located at a predetermined position over the magnetic disk together with the suspension (load state). When the rotation number of the magnetic disk reaches a predetermined number, the magnetic head slider is stabilized in a state of slightly floating over the surface of the magnetic disk due to the balance of positive pressure and negative pressure. Thus, the information is accurately recorded and reproduced.
In recent years, with a progress in higher recording density (higher capacity) of the magnetic disk, an improvement in performance of the magnetic read write head and the magnetic disk has been demanded. The magnetic disk is a discontinuous medium including collected magnetic microparticles, and each magnetic microparticle has a single-domain structure. In the magnetic disk, one recording bit is configured by a plurality of magnetic microparticles. Since the roughness of a boundary between adjacent recording bits is necessary to be small in order to increase the recording density, the magnetic microparticles need to be made small. However, if the magnetic microparticles are small in size, thermal stability of the magnetization of the magnetic microparticles is lowered with decreasing the volume of the magnetic microparticles. To solve the difficulty, increasing magnetic anisotropy energy of the magnetic microparticle is effective. However, increasing the magnetic anisotropy energy of the magnetic microparticle leads to increase in the coercivity of the magnetic disk. As a result, difficulty occurs in the information recording using the existing magnetic head.
As a method to solve the above-described difficulty, a so-called thermally-assisted magnetic recording has been proposed. In the method, a magnetic recording medium with large coercivity is used, and when information is written, heat is applied together with the magnetic field to a portion of the magnetic recording medium where the information is recorded to increase the temperature and to lower the coercivity, thereby recording the information. Hereinafter, the magnetic head used in the thermally-assisted magnetic recording is referred to as a thermally-assisted magnetic recording head.
In the thermally-assisted magnetic recording, near-field light is generally used for applying heat to a magnetic recording medium. For example, in Japanese Unexamined Patent Application Publication No. 2001-255254 and in Japanese Patent No. 4032689, disclosed is a technology of allowing frequency of light to coincide with a resonant frequency of plasmons which are generated in a metal, by directly applying light to a plasmon generator, in order to generate near-field light. In the method of directly applying light to a plasmon generator, however, the plasmon generator itself overheats and accordingly deforms, depending on usage environment or conditions. Therefore, practical realization of the method is difficult.
As a technology capable of avoiding such overheating, in Japanese Patent No. 4104584, a thermally-assisted magnetic recording head using surface plasmon polariton coupling is proposed. In this technology, without direct application of light propagating through a waveguide (guided light) to a plasmon generator, the guided light is coupled to the plasmon generator through evanescent coupling, and surface plasmon polaritons generated on a surface of the plasmon generator are used. To achieve higher recording density (higher capacity) from this time, near-field light with higher power density needs to be generated stably. However, since the thermally-assisted magnetic recording head which is now proposed uses a transverse-magnetic (TM) wave, it is actually difficult to provide high output of 100 mW or larger, for example. Accordingly, a thermally-assisted magnetic recording head which is capable of achieving higher recording density and has high operation stability is expected to be developed.